The Washington State Convention Center in downtown Seattle is eyeing a group of properties that - if acquired - would dramatically increase its footprint and its ability to host more and larger conventions.

The convention center is "definitely" looking at the two acres around Boren Avenue and Olive Way occupied by Honda of Seattle, said Jeff Blosser, president and CEO of the convention center public facilities district, or PFD. The acquisition would give the PFD enough land to build a subterranean expansion across several square blocks.

For years, the convention center has wanted to expand.

Five years ago, convention center officials began looking at options. They identified the full block over the Convention Place Station transit stop, which is partially underground at Ninth Avenue and Pine Street, as a place to grow. But the expansion plans have grown even bigger now to perhaps also include the Honda property.

Honda currently leases its site from Cassieford Co. and is relocating to Seattle's Sodo district, said Brad Miller, co-owner of Miller Nicholson Inc., which owns the dealership.

Cassieford is controlled by members of the Riach family, which operated car dealerships on the property for five decades until 1986. Honda's lease expires in 2014, and Cassieford has hired Jones Lang LaSalle brokers Stuart Williams, Ann Chamberlin, Lori Hill and David Young to market the property for sale, according to an offering memorandum. Williams declined to comment.

There's a long way to go before the convention center expands.

The convention center has learned from experience that funding can be fickle. That's what happened five years ago when funding from the state for the project fizzled, Blosser said.

The expansion plan "just kind of died a little bit" during the recession, and the center's board last year began to think again about the Convention Place Station site. King County Metro owns the site and considers it a prospect for housing or commercial development above the transit station.

According to its website, King County Metro Transit said a preliminary market analysis shows development on the site would be financially feasible.Convention center officials envision building three or four levels of exhibition space over the transit station as well as a level underneath it, Blosser said.

On the Cassieford property to the north and east, Blosser said, the convention center could add space underground and sell the property above it to developers who, under current zoning, would be allowed to build office and residential towers up to 400 feet tall.

Under this scenario, a level of underground exhibition space would stretch from Pine to Howell streets, Blosser said. The district is working with LMN Architects of Seattle to study the feasibility of the ambitious plan.

"We are going to spend the rest of 2013 trying to figure it out," said Blosser, who added convention center officials have not included private developers in discussions about what the center might do with the Cassieford property.

If the expansion plan proves feasible, the public facilities district would get "pretty serious," and draw up plans and get permits in 2014, he said.Funding for the project would come from the 7 percent lodging tax that's collected by hotels and motels in Seattle, said Blosser.

Last year, the tax generated a little more than $52 million for the convention center, up from nearly $50.5 million in 2011.Expanding the convention center would not be cheap. But in the convention business, size matters.

At stake are millions of dollars of business a year for hotels, restaurants and stores that cater to convention delegates - an increased number of delegates if the convention center can expand to host larger and more conventions.

Seattle's convention center, which straddles Interstate 5, is "basically the smallest on the West Coast in our competitive set," Blosser said.

Due to the lack of space, Tom Norwalk, president and CEO of Visit Seattle, said the center has turned away "almost as much business as we are booking. Just in the last three years, it's approximately a billion dollars worth of business turned away." Nonprofit Visit Seattle, formerly Seattle's Convention and Visitors Bureau, markets the convention center and handles direct sales for it.

This year, the center is scheduled to host conventions that will bring 175,000 delegates to town. Last year, events at the center drew around 160,000 delegates, Norwalk said.

Conventions are "a critical part of our tourism infrastructure," said Norwalk. From 1988, when the convention center opened, through 2011, spending by out-of-state convention delegates totaled $4.2 billion.

More than 12,000 people are expected to attend the May 1-10 Association for Research in Vision and Ophthalmology convention in Seattle. Norwalk said this will fill 29,355 hotel room nights and contribute $29 million to the local economy.

Having a bigger convention center means the ability to have more such conventions. The convention center has 205,000 square feet of exhibition space.Expanding over the Convention Place Station would add up to 200,000 square feet of space, and building under the Cassieford properties would create another 100,000 square feet, for a total of 505,000 square feet.

"Even with the expansion, we'll still be relatively small," Norwalk said.

San Francisco's Moscone Convention Center has 540,000 square feet of exhibition space, but has plans to expand. Last month, San Francisco lawmakers approved a plan that will provide key funding to add 200,000 square feet of exhibition space. Las Vegas hosts the largest convention center on the West Coast with 1.94 million square feet of exhibition space.

But any additional space "would be really a tremendous asset" for Seattle, Norwalk said, "because we know we are turning away that business now."mstiles@bizjournals.com | 206.876.5406